leases: split up generic_setlease into lock/unlock cases

Eventually we should probably do the same thing to the file operations
as well.

Signed-off-by: J. Bruce Fields <bfields@redhat.com>
vfs: fix handling of lock allocation failure in lease-break case

Bruce Fields notes that commit 778fc546f749 ("locks: fix tracking of
inprogress lease breaks") introduced a possible error pointer
dereference on failure to allocate memory.  locks_conflict() will
dereference the passed-in new lease lock structure that may be an error pointer.

This means an open (without O_NONBLOCK set) on a file with a lease
applied (generally only done when Samba or nfsd (with v4) is running)
could crash if a kmalloc() fails.

So instead of playing games with IS_ERROR() all over the place, just
check the allocation failure early.  That makes the code more
straightforward, and avoids this possible bad pointer dereference.

Based-on-patch-by: J. Bruce Fields <bfields@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
userns: Use uid_eq gid_eq helpers when comparing kuids and kgids in the vfs

Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
FIX fs/namei.c as should be.